1. Field of the Invention
The present invention relates to a roller bearing assembly that can be applied where a large load bearing capacity is required within a limited space, such as including a bearing assembly for supporting big and small ends of a connecting rod in an engine, a bearing assembly for a transmission, a bearing assembly for use in car air conditioners, a bearing assembly for use with a seat reclining mechanism and a bearing assembly for use in reduction gear units.
2. Description of the Prior Art
The roller bearing assembly has hitherto been well known, of a type in which neither an inner race nor an outer race is employed and a row of rolling elements are held in direct contact with inner and outer peripheral surfaces of operating elements of a device or equipment. This type of roller bearing assembly is generally referred to as a roller and retainer assembly or a caged roller assembly. In order to avoid accidental separation of some or all of the rollers from the roller retainer prior to the roller bearing assembly incorporated in a machine or equipment, the roller retainer used in this roller and retainer assembly hitherto largely employed has a generally M-shaped cross section, including an inner annular member of a diameter smaller than the diameter of the pitch circle of the rollers and an outer annular member of a diameter greater than the pitch circle diameter.
However, the M-sectioned roller retainer has pillars that lie on the pitch circle where the neighboring rollers are positioned closest to each other and, therefore, an attempt to increase of the number of rollers that can be accommodated within a limited space requires reduction of the circumferential width of each of the pillars left between the neighboring pockets. Accordingly, not only is the machining limit of the roller retainer encountered with, but the strength of the roller retainer tends to decrease.
In order to alleviate the foregoing problems, the roller and retainer assembly has been suggested, in which outer and inner annular members are positioned radially outwardly and inwardly of the pitch circle, respectively. See, for example, Japanese Laid-open Patent Publication No. 2000-179544. According to this known roller and retainer assembly, since no pillar of the retainer lie on the pitch circle where the neighboring rollers are positioned closest to each other, the pitch between the neighboring rollers can be reduced to permit an increase of the number of the rollers that can be accommodated in the retainer and this is indeed in contrast to the conventional roller retainer of the M-shaped section discussed above.
As an improved version of the roller retainer disclosed in the above mentioned Japanese patent document, the retainer has been suggested, in which a single split region is provided in the inner member at a location circumferentially thereof, so that the assemblability of the inner member can be increased. See, for example, the Japanese Laid-open Patent Publication No. 2003-166540.
On the other hand, Japanese Laid-open Patent Publication No. 2005-249163, filed in the name of the assignee of the present invention, discloses the roller and retainer assembly which includes a roller retainer made up of inner and outer members, each made of a resinous material, and having a plurality of circumferentially spaced slits each being of a shape cut-in inwardly from one side edge towards the opposite side edge.
The roller and retainer assembly disclosed in the first mentioned Japanese patent document includes an outer member and an inner member, in which the pillar between the neighboring pockets defined in the outer retainer has a rectangular cross-sectional shape. Accordingly, when an attempt is made to reduce the pitch between the neighboring rollers to render the resultant roller and retainer assembly to have an increased load bearing capacity, the plate thickness cannot be increased with no decrease of the strength, rendering the strength of the retainer to be low.
On the other hand, the roller and retainer assembly disclosed in the second mentioned Japanese patent document, that is, of the structure in which the split region is employed in the inner member at a location circumferentially thereof, a problem tends to arise that when the retainer is made of a resinous material, no injection molding process cannot be employed, making it difficult to manufacture. In other words, the presence of the split region at the location circumferentially of the inner member render the roundness of the retainer to be degraded and, therefore, no injection molding process can be employed. For this reason, the inner member is generally manufactured by injection molding in a ring member having no split region, which is subsequently formed with a split region by means of a mechanical cutting process. Thus, the necessity of the mechanical cutting process increases the number of manufacturing process steps, resulting in increase of the cost of manufacture.
Also, opposite ends of the inner member on respective sides of the split region must be overlapped one above the other to render the inner member to have a size smaller than the diameter of the inscribed circle of the roller. Thereafter, the split region is engaged to restore the inner member to the original diameter. For this reason, no assembly can be achieved relying only on the elasticity possessed by the material of the retainer, resulting in low assemblability.